1. Field of Invention
The present invention relates generally to disease prevention in livestock, and, more specifically, to the prevention or alleviation of ascites in broiler type poultry.
2. Background
Ascites, also known as pulmonary hypertension syndrome, is a condition characterized by the accumulation of serous fluid in the spaces between tissues and organs in the abdominal cavity and is most prevalent as an affliction of poultry. The fluid is clear or amber in color, originates from the liver and has the general composition of plasma. Also referred to as waterbelly, high altitude disease and avian edema, ascites is attributable to the inability of the cardiovascular system to meet tissue oxygen demands.
The economic consequences associated with ascites are severe and occur due to a combination of increased bird mortality and condemnations along with reduced growth rate and feed efficiency. In the United States alone, annual poultry industry losses due to ascites are estimated to exceed 65 million dollars. Though estimates for dollar losses in other countries are not as readily available, the annual global impact of this disease likely exceeds a billion dollars.
In most cases ascites is brought about by a divergent bird oxygen requirement and its cardiovascular ability to supply oxygen as a nutrient. The inability of the cardiovascular system to meet tissue oxygen demands may result from may different circumstances, one example of which is a reduced atmospheric oxygen concentration. It was under these conditions in the 1970""s that ascites was first recognized as a disease in broiler flocks grown at high altitude in South Africa and South America. Birds initially compensate for reduced tissue oxygen supply by increasing cardiac output. However, problems arise when the return blood volume exceeds the capacity of the heart to pump the blood. As a result, the heart enlarges, becomes round in outline and develops a dilated right ventricle. The right heart failure causes increased vena cava pressure and liver congestion. Classic ascites ensues due to the increased hepatic hydrostatic pressure resulting in transudation of fluid through the liver capsule into the abdominal cavity. The chronically elevated intrahepatic pressure leads to loss of hepatic parenchyma, intrahepatic fibrosis (cirrhosis) and hepatic dysfunction.
Other factors contributing or predisposing poultry to ascites have been identified. Pulmonary tissue damage, such as caused by exposure of birds to dust and ammonia, as well as diseases affecting the lungs (e.g., infectious bronchitis, Newcastle disease, infectious coryza, colibacillosis, aspergillosis), is known to be associated with an increased incidence of ascites, as is reduced cardiac function. Excess furazolidone, toxic fat and excess salt in the diet are also predisposing factors, along with cold distress brought about by nonevaporative heat loss.
Despite a better understanding of the disease, there has been a dramatic rise in ascites incidence in recent years. Primarily responsible is the increased growth rate of today""s genetically engineered birds. The desire to achieve rapidly growing lean strains of meat chickens and the demands from processors to increase yields by reducing the overall size of visceral organs has meant a selection of strains susceptible to ascites. To put it in perspective, the age to slaughter and the amount of feed required to produce a given quantity of chicken meat has been more than halved since the early 1950""s. See Havenstein, G. B., P. R. Ferket, S. E. Scheldeler and B. T. Larson, Growth, Livability and Feed Conversion of 1957 vs. 1991 Broilers When Fed xe2x80x9cTypicalxe2x80x9d 1957 and 1991 Broiler Diets, Poultry Science, Vol. 73, pp. 1785-1794 (1994). In the early 1950""s the average length of time required to grow a broiler chicken to a 4 pound harvest weight exceeded 15 weeks. Through genetic selection, this time period has been reduced to a current average of about 6 weeks. Consequently, bird metabolic events that are needed to produce a unit of poultry meat have been squeezed into a shorter time period, creating a high metabolic demand in today""s bird. Such metabolic demand is further elevated by environmental factors, such as low and high ambient temperature, and disease. As a bird having a high metabolic demand possesses a higher oxygen requirement, severe stress is placed on the bird""s cardiovascular support system. The stress is exacerbated when gain composition consists primarily of protein gain, as is the case with broiler type birds. Studies by the inventors show that trial broilers consumed 3.1 liters of oxygen per gram of protein gain versus just 0.82 liters of oxygen per gram of fat over a 35 day production period. Thus, a bird""s ability to consume and transport oxygen not only has the potential to impact bird health via ascites, but also carcass composition by limiting protein synthesis ability.
The incidence of ascites in fast growing birds may be reduced by lowering gain accretion rate, such as by feeding low caloric density rations and restricting feed intake; however, lowering growth rate is not appealing to the poultry industry as it fails to maximize bird productivity.
There is thus a need for an aid to prevent or alleviate ascites in stressed, rapidly growing livestock, particularly poultry. The present inventors have discovered such an aid in a carnitine supplemented diet for poultry. The diet is unexpectedly effective at reducing the incidence of ascites (as evidenced in a reduced hematocrit, right ventricle weight and ascites heart ratio) in broiler type poultry and potentially enhances growth rate, feed efficiency, survivability and carcass quality.
In the patent art, U.S. Pat. No. 5,213,815 discloses a method of treating ascites comprising the administration of Eyebright herb and Brewer""s yeast to poultry in need thereof. In U.S. Pat. No. 4,970,080, ascites is purportedly treated by feeding small amounts of zeolite to the affected animal.
Heretofore, carnitine in poultry diet has been reported to have no beneficial effect on feed intake, body and abdominal fat weight or on carcass or liver lipid levels in growing broilers (Cartwright, Poultry Science, Vol. 65, Suppl. 1, p. 21, 1986). Dietary carnitine has been shown to retard ethanol metabolism in broilers (Smith et al., Poultry Science, Vol. 71, Suppl. 1, p. 64, 1992), and, in U.S. Pat. No. 5,362,753, to increase the hatchability of eggs.
Unrelated to poultry, carnitine has been used as a supplement in pig diets (U.S. Pat. Nos. 5,124,357 and 5,192,804 and PCT Publication WO 98/24328), a smolting feed for salmon (U.S. Pat. No. 5,722,346) and in a catfish diet (U.S. Pat. No. 5,030,657). The use of carnitine in the treatment of heart failure or myocardial ischemia is discussed in U.S. Pat. No. 4,075,352 and PCT Publication WO 98/43617.
Notwithstanding the known uses of carnitine, the prior art wholly fails to teach or suggest as disclosed and claimed herein a carnitine supplemented diet fed to broiler type poultry to prevent or alleviate ascites.